Process for extraction of phosphorus compounds

ABSTRACT

An extraction process for recovery of phosphorus compounds from both low and high grade phosphate ores utilizes a room temperature extraction with dilute mineral acids whose calcium salts are water soluble. Preferably the ore is coarsely ground. Dissolved impurities are removed from the dilute phosphate solution by a first neutralization step, whereafter further neutralization precipitates high purity calcium hydrogen phosphate. The latter may be converted to high purity phosphoric acid by treatment with sulfuric acid. Either lime or ammonia may be used advantageously as a neutralizing agent.

[ 51 Nov. 11. 1975 1 1 PROCESS FOR EXTRACTION OF PHOSPHORUS COMPOUNDS[75] Inventor: Douglas 0. Hauge, Moraga Calif.

1731 Assignee: United States Gypsum Comp-an Chicago, 111.

[22] Filed. Oct. 19, 1971 1211 Appl. No: 190,511

Related US. Application Data [631 Continuation-in-part ol' Scrl No. 91542. Nm lbv 19711. abandoned.

[521 US. Cl. 423/309; 423/311; 423/319; 423/167 151] Int. Cl. C(llh15/16; C011) 25/26; ((1113 25/16 [58] Field Of Search 1. 423/166, 167,317-3211 423/308-309 311 313 [56] References Cited UNlTED STATES PATENTS1013.970 9/1935 Moore 413/166 2 14.6110 4/1938 Larsson i l 423/3193150.957 9/1964 Seymour et all. ..r,..l 423/319 X 3.359.067 12/1967Henrickson et alums 423/166 3:111 1 .111-1 I/llhh Saeman 421 319 FOREIGNPATENTS OR APPLICATIONS 938.468 Ill/1963 LTnited Kingdom Primal-[5.1ammurOscar R4 Vertiz Aszw'xlum 1;.mrm'zwr-Gregory Av Heller.innrnvy. Age/11. or Fir'l11-Kenneth E. Roberts. Stanton T. HadleySamuel Kurlandsk} [57] ABSTRACT An extraction process for recovery ofphosphorus compounds from hoth low and high grade phosphate oresutilizes a room temperature extraction with dilute mineral acids whosecalcium salts are water soluble. Preferably the ore is coarsel ground.Dissolved impu rities are removed from the dilute phosphate solution bya first neutralization step where-after further neutralizationprecipitates high purity calcium hydrogen phosphate, The latter may beconverted to high purit phosphoric acid by treatment with sulfuric acid.Either lime or ammonia may he used advantageously as a neutralizingagent.

23 Claims. 3 Drawing Figures 9 0 RECOVERY U.S. Patent Nov.11,1975Sheetl0f3 3,919,395

ACID NORMALITY Fig. I

Douglas 0. Hauge INVENTOR.

John Kenneth Wi George E. Verhage Dana M Schmid ATTORNEYS US. PatentNov. 11, 1975 Sheet 2 of3 3,919,395

FIRsT J GFgCIJQUEND B R%4 C l 4 l4 SECOND ];2

LEACH I FILTER 03 WASTE DRUM 3 04 SUPER SILT POLISH sETTLER FILTER LEACHWASTE /O6 WASTE MILK OF LIME cRYsTALLIzER ISETTLER DICAL. I30HYDROCLASSIFIER sETTLE I22 WHZO J FILTER I D|CAL I60 sETTLER I H SOMIXER MIXER I Ol2 SETTLER H2O FILTER MAKE UP DOUGLAS 0. HAUGE GYPSUMINVENTOR BY I' Isfi IsIgtEY AN F I9. 2

KENNETH E. ROBERTS ATTOR N EYs U.S. Patent Nov. 11,1975 Sheet30f33,919,395

MOTOR /96 Fig. 3

DOUGLAS 0. HAUGE INVENTOR DANA M. SCHMIDT BY STANTON T. HADLEY KENNETHE. ROBE RTS ATTORNEYS PROCESS FOR EXTRACTION OF PHOSPHORL'S COMPOUNDSThis application is a continuation-inpart of Ser. No. 90.542. filed Nov.lts'. l97U and now abandoned.

BACKGROUND OF THE INVENTION Recovery of compounds of phosphorus inusable form from phosphorus-containing minerals is a long es tablishcdand commercially important industry. The phosphorus containing mineralwill be referred to herein as phosphate rock' or as phosphate ore."Phosphate rock contains \arying amounts of calcium phosphate (apatite)or fluoroapatite. The common impurities present in commercial depositsare silica and silicates. iron and aluminum oxides. limestone and fluorides.

Commercial phosphate operation in this country concentrate on the use ofdeposits of phosphate rock of relatively high purity. i.c.. high calciumphosphate content. These deposits occur principally in Florida, in thelower Appalachian regions and in the northwestern sections of thecountry. Two general classes of processes are used to recover phosphoruscompounds from phosphate rock. In one class of process. the phosphoruscontent of the rock is reduced to elemental phosphorus in an electricfurnace and the recovered phosphorus is burned to phosphorus pcntoxide.which is absorbed in water to form phosphoric acid. The other classconcerns the so-called wet processes. in which phosphate rock is treatedwith an acid to release phosphoric acid and precipitates. Most of thewet processes are well summarized in US. Pat. No. 3.494.735. a patentwhich itself discloses yet another wet process. That is, the most commonwet-process system is known as the Dorr-Oliver Strong Acid Processinvolving the following reaction:

6H PO lU(CLtSO 'ZH ,O) ZHFT Less than furnace grade phosphoric acidresults. The Israeli Mining Industries process uses the followingreaction:

iocacl ZHFT Liquid-liquid extraction removes the phosphoric acid. TheDow Chemical process taught in US Pat. No. 3.072.461 proceeds asreaction No. 2 above. but uses fractional distillation to isolate thephosphoric acid.

- en po,

The St. Paul Ammonia Co. process is essentially as follows:

3. [CA ,(PO ];,'CaF ZOHNO 6H PO;

10cm no. ZHFT using a liquid-liquid extraction to isolate the phosphoricacid. Finally. the wet process of the aforesaid U.S. Pat. No. 3.494.735uses hot (about l0UC) phosphoric acid to leach the phosphate values fromthe apatite. monocalcium orthophosphate being precipitated by coolingthe solution to a temperature between 70C and 85C. Impurities areremoved by a cationic ion exchange resin. The reactions are as follows:4. lCa-dPO bl -CaF 14H;;PO,

iocarn Po. l n o ZHFT 5. RH: Ca( H POdyH O RCa ZH PO H O It should benoted that all of the above prior art wetprocesses are characterized byuse of relatively high grade ore and the production of HF gas as aby-product. For example. the aforesaid US. Pat. No.

oil

2 3.494.735. gives as its example a treatment of rock bearing as much PO as 39.602. High temperature operation and/or fine grinding of the oreis also a characteristic of these processes.

Other reference to the development of phosphoric acid processes and thepresent state of the industry can be found in the literature. such as"Phosphoric Acid." by A. V. Slack. volume 1. part 1 (Marcel Dekker. lnc.New York 1968 As is to be expected in an industry of the age andcommercial importance of the phosphate industry. such literature on waysto recover useful phosphates from phosphate rock is \oluminous and c\ ensomewhat confusing. It should be noted. however. that some processeshave been developed for treatment of unground. low grade phosphate ore.For example. US. Pat. No. 1.969.95] discloses in effect a multiple stageleaching ofunground. low-grade ore by the use of dilute HCl absorbedfrom a byproduct gas. lmpurities such as CaF: are precipitated from thepregnant liquor by adding finely phosphate rock. Dical is produced byadding milk of lime.

None of these abovcanentioned prior processes recognize that thepresence of R 0 impurities in the ore requires special leaching steps inorder to minimize the amount of these impurities which are dissolved bythe acid. Failure to exert such care either results in removal of thedissolved impurities as phosphates. thus lowering the percentage ofrecovery. or the impurities remain in the calcium phosphate product.whatever its form. thus reducing the grade level at which it can besold. Also. it should be noted that the best of these prior wet processtechniques can not recover more than about 75% of the phosphate in arelatively pure form.

As noted above. other acids. such as hydrochloric and nitric. arementioned in the literature as being of utility in phosphate processingoperations. Ne ertheless. it appears that only an Israeli process usingstrong hydrochloric acid has reached commercialization.

OBJECTS OF THE INVENTION It is the primary object of the invention toattain a process for recovery of useful very pure phosphorus compoundsfrom low purity phosphate rock.

It is a further object of the invention to provide an cs sentiallypollution-free process for recovery of phos phate values from phosphaterock wherein no volatile fluorides are evolved. there are no phosphateslime ponds. and wherein the gypsum coproduct is of commercial utility.

It is a further object of this invention to provide a room temperatureprocess for treating low purity phosphate rock.

It is a still further object of the invention to dissolve the phosphatevalues from the rock with dilute hydrochloric acid in a fashion whichminimizes dissolution of impurities.

Another object of the invention is to provide such a process which maybe operated either in batch fashion or continuously.

A further object of the invention is to treat the phosphate ore withdilute acid in two stages. in which a dilute acid is used for initialcontact with the ore and in which a more concentrated acid thereafter isused for leaching of phosphates from the partially extracted rock.

It is an additional object of the invention to provide a process forvery high percentage recovery of relatively pure phosphate values fromlow grade phosphate ores 3 using dilute mineral acids whose calciumsalts are ei ther water or dilute acid soluble.

It is a still further object of the imention to avoid foaming in theleaching operation by using the final leach solution (spent acidsolutionl containing the dissolved phosphates to moisten the ore as itis fed to the leaching step. thus decomposing the carbonates containedtherein.

A further object of the invention is to increase the pH of the acidsolution after leaching in two stages. in which the first increase iseffected by addition of a calcium phosphate slurry of pH less than 7.

It is a still further object of the invention to adapt the presentprocess to the extraction of phosphate values from so-called highgradeores. without necessity for prior beneficiation thereof.

Still another object is to separate a highly purified phosphate compoundfrom ore so impure as to be otherwise undesirable. without driving offpolluting impurities.

A further object of the invention is to provide a process which willmaximize the size of crystals of the end products. thereby increasingthe efficiency of recovery of the end-products from the carrier liquid.

Other objects and advantages will become apparent upon reference to thefollowing drawings and detailed discussion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a chart depicting therelationship between normality of the acid leach and percent recovery ofthe phosphate valucs'.

FIG. 2 is a flow chart of the preferred process of the invention; and

FIG. 3 is a sectional view of the crystallizer used in the process shownin FIG. 2.

GENERAL DESCRIPTION OF THE INVENTION In diametric opposition to thestatement on page 19 of the Slack book above referred to. If rockcontains enough impurity to reduce the grade to less than 66 BPL (30.2%P it is generally considered to be uneconomical." the process of thisinvention is designed to operate on phosphate rock containing as littleas 5% P 0 sometimes even less. The specific combination of process stepsinvolves the use of a very coarsely ground feed. as conventional finegrinds would pose an insuperable filtration problem to remove therelatively high proportion of impurities. Preferred in a grindcontaining not over about ltlf'l minus 200 mesh material. Preferably. atleast about two thirds should be coarser than ltlt) mesh. It involvesthe use of dilute hydrochloric or nitric acid (preferably 3.35NJ atambient temperatures. A further requisite is the avoidance of thevigorous agitation of the rock-acid mixture characteristic of someconventional processes. By operating in this fashion. insolublematerials remain in a reasonably readily tilterable or separablecondition. The phosphate values are recovered from the solution afterseparating out as by filtering. the impurities in a two-stagespecification with lime or ammonia. in each of which close control of pHis a requisite. In the first precipitation, the pH is raised to about Ito 2. at which point the dissolved impurities largely precipitate andsome calcium phosphates are also precipitated. At the higher pH levels.greater efficiency of impurity precipitation is achieved. The secondprecipitation involves the further addition of lime or ammonia to raisethe pH to a level of about 35. L'nder these conditions calciumphosphates in purity adequate to be satisfactory for feed grade productsare formed. The linal liquid from this process is a solution of calciumchloride (where HCl was the starting acidl of about Ill-15Mconcentration and a pH not exceeding about b. At this concentration.recovery of hydrochloric acid is readily possible by addition ofsulfuric acid to precipitate calcium sulfate. (where lime has been theinitial precipitant). the latter coming down under these conditions as areadily tilterable material. The hydrochloric acid may then be returnedto the process. If desired. the purified calcium phosphates recoveredmay be treated with sulfuric acid to form high quality phosphoric acid.or other products.

Additionally important in the process is the necessity of maintainingthe phosphate concentration in the solutions at a relatively low level.as this facilitates removal of impurities and helps militate againstexcessive losses of phosphate values with the impurities. Specifically.it is preferable to maintain the concentration ofdissolved phosphates inthe extraction solutions at not exceeding about 7%. calculated as P 0and preferably in the range of 35% As indicated hereinabove. the processmay be operated either as a batch process or as a continuous process.Each will be illustrated in the specific examples which follow. and itwill be appreciated that certain advantages accrue to each. although forcommercial purposes the continuous process is preferred. One advantageof the continuous process is that the small amounts of alkali metalcompounds present in the low grade rock tend to accumulate in therecirculating leaching acid. This facilitates precipitation offluorideimpurities as calcium fluoride, or sodium and potassium fluosilicate.there being sufficient siliceous material dissolved to permit thisreaction. These compounds are quite insoluble. and this reaction thusrepresents a very satisfactory way to reduce the fluoride impurities.This is a marked advantage over present-day commercial practices. inwhich volatile fluorides are evolved.

The amount of acid used should be at least stoichiometric.Theoretically. complete conversion of fluorapatite to calcium chlorideand phosphoric acid requires 1 .71 parts by weight of hydrochloric acidto one part by weight of P 0 If. however. the reaction products aremonocalcium phosphate CaH ,t PO J and HF. then the hydrochloric acidrequirement is 1.20 weight units per weight unit of P- ,O contained inthe ore. This latter salt has a pH in solution of about I. Additionalacid is required to react with the carbonates and with the other calciumcompounds in the ore. such. for example. as calcium hydroxy fluoride.Experience has shown that a usage of hydrochloric acid of about I .5 ormore weight units per weight unit of P 0 in the ore is the most advantageous ratio of acid to use. Less total acid is required when theleaching is conducted counter-current in a continuous process.

In a variant of the process. the ore may be treated with dilute acid. ashereinabove described. and a crude separation effected. in which thecoarse material insoluble in the acid constitutes one fraction and aslurry of the fines in the acid solution constitutes and the otherfraction. The partially leached coarse fraction may thereafter beleached with a stronger acid and washed with water to aid in recovery ofdissolved phosphates.

and the wash water added to the stronger acid. which is then returnedfor contact with the starting ore. In a further variant this dilutestronger acid may first be used to treat the fine materials separatedfrom the leach solution for additional dissolution of phosphate values.This is especially advantageous. as. perhaps due to electrostaticeffects. the fine materials settle out quite rapidly from a suspensionin this acidic solution. They may be removed. washed with water and thewash water added to the diluted stronger acid. and this twice dilutedacid may constitute the dilute acid solution brought into contact withthe starting ore.

When nitric acid is the dissolving acid. and lime is used in thepH-increasing steps. the nitric acid may be regenerated from the finalcalcium nitrate solution by precipitation of gypsum by addition ofsulfuric acid. If ammonia. on the other hand. is the neutralizingmedium. either ammonium nitrate may be recovered or ammonium sulfate maybe recovered with conversion to nitric acid of the nitrate moiety forreturn to the process. Both ammonium sulfate and ammonium nitrate arevaluable products in their own right.

Recovery of the phosphate has been remarkably high and of a remarkablepurity. At least 80% recovery is standard in the operation of theinvention. the phosphate having the purity of furnace grade" or better.dicalcium. phosphate.

SPECIFIC EMBODIMENTS OF THE INVENTION EXAMPLE 1 In this Example. theresults of which are depicted graphically in FIG. I, a determination wasmade of the relationship between normality of acid used to leach the oreand the efficiency of recovery of phosphate values therefrom. The sameore was used in each of the tests. It was a low grade ore containing 8%P and was coarsely ground. In each case 50 milliequivalents of acid wereused per gram of P 0 in the sample. Acid normalities of the HCl usedrange from 2 to 6. The ore samples were stirred with the volume of acidsolution requisite to provide the above-specified total amount of acidand were allowed to stand quiescent at room temperature for minutes. Thesamples were filtered. washed with water. and the phosphate valuesrecovered were determined by analysis of the filtrate.

As will be seen by inspection of FIG. I, the results show a somewhatbell-shaped curve. with maximum recovery at an acid normality of about3. In the 2.3-5N range. recoveries are above 80% under the testconditions. but drop off rapidly as the normality is above or belowthese limits. This efficiency of recovery exceeds that realized inpresent commercial processes when yields are computed on theunbeneficiated ore.

Leaching with dilute nitric acid gave similar results.

EXAMPLE 2 Low purity phosphate rock having the analysis:

was ground in a swing hammer mill. and oversize mate rial was separatedby a Hummer screen and returned to the mill. The ground product had ascreen analysis of r l 4 mesh UH *l-l mesh -10 mesh 73" -18 mesh 03H ol)mesh 37') i l UH mesh In.

The ground rock was fed. at a rate of It) lbslmin. to a substantiallyhorizontally mounted drum rotating at about 4 rpm. The drum was equippedon its interior walls with a number of vanes to lift the material contained therein and then to let it drop. to provide gentle.non-attritiona] mechanical agitation. Also fed into the drum along withthe ground rock was dilute aqueous hydrochloric acid (3N). at a feedrate of l.7 gal. per minute. (51.5 M.E./G.P O,-,)

The effect of the gentle agitation in the drum was to retain the coarseparticles in the drum in contact with the acid for a somewhat longertime than the residence time of the finer particles. Average residencetime was 18 min.. and this leaching operation was conducted at ambienttemperatures. Recovery of phosphate value was 98% or higher.

The coarse material leaving the leaching drum. together with some of theacid liquor. was deposited directly on a belt filter. The bulk of theliquor. containing some fine material in suspension. was fed to thefirst of two series arranged settling tanks. the overflow from the firsttank discharging into the second. The concen trated slurries offinematerial (herein sometimes called silt) which accumulated at the bottomsof the steel ing tanks were pumped to the belt filter and depositedthereon at an intermediate point. at which a filter cake of the coarsematerial had already accumulated. The supernatant liquor overflowingfrom the second settling tank had a pH of 0.8. Water was used to washthe cake on the belt filter.

The filter cake. consisting of the coarse material (principally sand)and the silt (also principally sand) was about 23% moisture and amountedto olbs dry solids per minute. (1 lb. per min. superslit left insystem.)

To the leached phosphate solution (5% Pv ,O,-.) was added (firstprecipitate) milk of lime at the rate of 1.8 gram Ca(OH) per IOU ml.leached solution. This reaised the pH to 2 and caused precipitation ofimpurities (calcium. aluminum and iron salts and fluorides). which wereseparated.

The thus purified filtrate was treated with (second precipitate) milk oflime at the rate of 2 grams Ca- (OH) per 100 ml.. which raised the pH to3.5 and caused precipitation of substantially all of the phosphatevalues as calcium phosphate (principally calcium hydrogen phosphate.often called dical). The precipi tatcd calcium phosphate was separatedby filtration on a belt filter. After drying. it had the followinganalysis:

39.492 P 0 Theory for 100% dical (dicalcium phosphate dihydrateCaHPO,,.2H O) is M2471 P 0 and 23.29% Cav Recovery rate of calciumphosphate was 2 lbs/min.

The filtrate was principally an aqueous solution of CaCl The CaClconcentration was 4.5% as Ca.

Gypsum of high purity was recovered from the CaCl solution by adding anapproximately stoichiometric quantity of sulfuric acid. The precipitatedgypsum was of food grade. lt was recovered by filtration and thefiltrate (hydrochloric acid solution 3N] was sent to a stor age tank forreuse.

EXAMPLE 3 A variant of the continuous process described in Example Z isillustrated in this example. In this example. two leach drums were used.the drums being arranged in series. In each case. the drums weresubstantially horizontally mounted and rotated slowly. As in thepreceding cxample. vanes affixed to the interior walls of the drumslifted the material and dropped it gently back into the bottom peripheryof the drum. A little of the final acidic phosphate solution was used tomoisten the rock fed to the first drum to avoid lumping. and also todecompose carbonates in the feeder. thus minimizing foaming in the leachdrums. A pug mill was used to provide a positive feed of the moistenedground rock. The first leach drum operated on a counter current basis.with the moistened ground rock being fed to one end of the drum and anintermediate acidic phosphate solution (to be later described) was fedto the opposite end of the drum. The counter-current action removed theliquid containing some fine particles suspended therein from the firstend of the drum. while from the second end of the drum emergedprincipally the coarser particles of rock. partially extracted. Thesecoarser particles had an analysis of 4.3% P 2.6% R 0 and .89? fluorine.This is to be compared with 84)? P 0 3.0% R 0;; and LUJ'? fluorine inthe starting rock. The coarse particles were fed to the second leachdrum co-currently with a stronger acid solution. (6 normal HC l). Thesolids and the liquor were separated as they emerged from the oppositeend of the second drum. and the solids were washed with water. and thewash water was added to the fine particles already separated from thepregnant liquor. the wash water having a strength of about 3.4 normal.The suspension emerging from the first end of the first drum wasseparated by settling. and the fine solids were then suspended in the3.4 normal liquor from the second drum. They were re moved and washedwith water and the wash water was added to the liquor. This liquor.which had a normality of 3. is the liquor which is fed countercurrent tothe second end of the first leach drum. The coarse solids removed fromthe second leach drum contained .U39'r P 0 1.5% R 0 and 0% fluorine.

It will be seen that the partial removal of phosphate values in thefirst leach drum permits use of somewhat stronger acid in the secondleach drum for more effec' tive penetration of the coarse particles.without producing a solution which is so concentrated that some of thephosphate product would reprecipitate. Further. it has been discoveredthat the fines are the source of most of the R 0 impurities. and theabove separation ofthe fines prevents the stronger acid from acting onit.

The acidic phosphate liquor recovered as indicated above was treatedwith a pH 6 slurry containing dis solved phosphates. as well asprecipitated calcium phosphates. The amount thereof was sufficient tobring the solution pH to 3. Dical precipitated and was recov ered byfiltration. The supernatant liquor was treated with lime water to pH 6.thus forming the material used for the initial neutralization describedabove.

This procedure has an advantage over direct addition of lime water tothe acidic phosphate solution. in that in the latter the very stronglyalkaline character of the lime tends to form precipitates with a core oflime or tricalcium phosphate. surrounded by phosphates of lesserneutralization. A purer precipitate is produced by the precipitationdescribed in this example. In this example. it has also been foundadvantageous to use the recovered calcium chloride solution or water assuspending agent to produce the lime water slurry used in the limingstep.

The hydrochloric acid can be regenerated from the calcium chloridesolution. with the co-recovery of gypsum. as described in the precedingexample.

EXAMPLE 4 Still another variant. which is the preferred embodiment ofthe process. is shown schematically in FIG. 2. This example is similarto the preceding one. Like the previous embodiments. the ore is onlycoarsely ground and is fed into. in succession. first and second leachdrums l0 and 20. Unlike the previous embodiment. the dilute acid ofabout 0.2 normality indentified as line Al and having a pH of about 0.5.is not added at the opposite end 12 of drum but rather is added to theore as it is fed into the drum by a pug mill. not shown. The function ofthe pug mill is to blend the weak acid with the ore so as to break downthe minute gas bubbles which otherwise form under the action of the acidand cling to the ore. preventing the ore from mixing properly in theleach drum. This dilute acid is primarily phosphoric acid. as in theprevious embodiments. The drum is slowly rotated (about 4 RPM) andtilted so that the overflow 01 comes out the incoming end 14, carryingwith it the silt and supersilt and the easily extract able phosphates.The inclination of the both drums from the horizontal is approximatelyone-half inch per footv Most of the R 0 impurities are carried out asultrasilt or included therein. This material is separated in settler 50and the liquid becomes the underflow U1 from the silt settler 50.hereafter discussed. and fed into the second leach drum at its first end22. The stronger acid A2 is fed countercurrent at the opposite end 26.This acid is an 8% solution of HCl including about 0.5% by weight gypsumfines. which is recycled from a subsequent treatment hereinafterdescribed. The per cent concentration of acid A2 preferably does notexceed about 8% so as to minimize any tendency to dissolve anyimpurities introduced by underflow U1. Overflow 02 from drum 20 carrieswith it the remaining phosphate values dissolved therein. along with thegypsum fines and some fine grade sand. Settler removes the sand andcombines it with the spent sand 32. All this sand is then separated fromliquid by a filter 40. which may either be a belt filter or a rotaryfilter. and dumped as a waste. The gypsum fines introduced by acid A2come out in the overflow. which latter is divided into two streams O3and Al. The splitting of this overflow accomplishes two things. First itprevents flooding of drum 10 which would undesirably reduce theresidence time of the fines and ultrafines below the approximate 15minutes which is desired. and secondly it introduces directly into thesilt settler some of the gypsum finesv It has been discovered that thesefines (about 50 to 200 microns in size. the larger being acceptablebecause they disintegrate in the solution) are necessary to maximize thesettling of the silt and u]' trasilt at settlers 50 and 60.respectively. These fines are about 90% of the input to settler 50.Although the mechanism of this phenomenon is not completely understood.it is thought that it is similar to the known effect which calcium ionshave in the precipitation of clay. As mentioned above. the silt inunderflow Ul is added to the first extracted sand 16. This silt is inthe 100 to 200 mesh size.

Overflow O4 carries with it the dissolved phosphates. the supersiltwhich includes R impurities and CaF introduced by O] and O3. and 0.59?gypsum fines. to the supersilt settler 60. The supersilt extracted hereas underflow U2 includes the impurities C aF and R 0 and silica. Theimpurities R 0 and CaF are to some minor extent also dissolved in O4.and these are precipitated out at settler 60 by the addition. describedbe low. of underflow U4. Extracts U2 can be dumped with the waste fromfilter 40, or it can be filtered separately for agricultural(fertilizer) uses. or converted into acid.

From settler 60, overflow O5 is essentially free from suspended orentrained solids. with the exception of fine silicas in a colloidalsolution. It has been found that this colloidal solution must be removedif large size product crystals are to be recovered. lt has beendiscovered that a polishing filter 70 using gypsum as the filteringmedium is very effective in removing this collodial solution. Any lengthgypsum crystals are suitable for this. Overflow O6 therefrom ischaracterized by a sparkling clear appearance. and is the pregnantliquor with the desired phosphate values lts pH at this point is about1.0.

Turning now to the dical production stage in the process. the pregnantliquor is carried to crystallizer 80. the details of which are set forthbelow. Saturated milk of lime with a pH of about and an excess ofOHradicals is introduced into the crystallizer in a counter-current,finely dispersed mixing action. It is necessary to keep the percent ofphosphate above 1% in this reaction. to insure that the precipitate isdicalcium phos phate rather than tricalcium phosphate. To maximizecrystal growth and thereby aid in recovering the dical crystals, thetemperature of the crystallizer must be maintained between 120l25F andgently agitated (about RPM). The dical slurry 110 so produced is takento a settler 112, where the overflow O7 is the CaCl produced by thecrystallizer. which is then optionally reacted to produce gypsum.Underflow U3 is still a dical slurry. although more concentrated. andthis proceeds to hydroclassifier 120. This classifier conventionallyintroduces a water back wash 122 from settler 130 to carry off asoverflow O8 fines still in the slurry U3. These fines include finecrystals of dical. and are in the size range of between about l0 andmicrons. These fines are separated by settler 130 and are extracted asunderflow U4 which is returned as a fine slurry of dical to settler asdescribed above. Underflow U4 raises the pH in settler 60 to about 1.thus causing any dissolved impurities such as CaF R 0 and monocal toprecipitate. The underflow also raises the P 0 content in the pregnantliquor.

Overflow O9 and 010 are each a weak dical slurry of a pH of betweenabout 3.5 and 5. The O9 portion is returned to be combined with the milkoflime and 010 is used as a gypsum wash described below. Underflow U5 isthe dical product which is conventionally filtered at 140 and recovered.The water wash which is run through filter 140 is sent to the settlerwhere the liquid component is added to the overflow 122.

lt is important to note in this decal processing that. unlike prior artmethods. it is not necessary to add lime or a water-soluble base. tosettler ll2 to cause adequate separation of the dical. This is due tothe increased crystallization efficiency provided by the efficientmixing action of the crystallizer described below.

It is further important to note the manner in which this process keepsimpurities to a minimum. Specifically. the R Q, impurities must beseparated from the action of the stronger acid supplied by line AZ. Thisis rendered possible by the separation of the fine portions of the orein drum l0. and the removal of the tines by overflow 01. As the R 0impurities are by and large supersilt. these are carried out by overflowO4 to settler 60, rather than as underflow Ul which does receive thestronger acid leach in drum 20. Also. any dissolved R 0 impurities arecontained in overflow O4. and precipitated out at settler 60 due to theincrease in pH caused by the addition of underflow U4 thereto. As to theCaB impurities. these can be and are leached out in a minor degreeand/or carried as silt from either leach drum. but in any event arecollected by settler 60 par ticularly due to the increase in pH causingtheir precipitation. Thus. the dical which comes from filter H0 has avery high purity.

Turning now to the formation of by-product gypsum. this step is followedprimarily to recover the leach acid HCl necessary in leach drum 20. andis primarily a conventional process with the following exceptions.First. the sulfuric acid must be added to mixer [50 in a preferred ratioand at a preferred mixing temperature to achieve optimum crystal growth.Also. maximum growth is achieved by maintaining rapid and intimatemixing. For example. it has been discovered that operation of mixer 150at 10C produces crystal sizes of around 10 microns. at 45C producessizes between about 50 and microns. and at 65C produces sizes of betweenabout [00 and 200 microns. Above 65C. the HCl resulting from thereaction tends to vaporize rather than be recovered. As to the optimumion ratio. it has been discovered that larger needle-like crystals areproduced if C] ions in excess of the stiochiometric amount are provided.More specifically. if an equal volume of HCl having the same normalityas the C aCl is added to the latter before adding 96% concentrated H 50a lower moisture content is provided by the gypsum crystals formedthereby. than would be the case if the dilution" of the Ca did not takeplace. (See the Table below).

The moisture content is an inverse measure of the crystal length. as thelonger crystals do not pack well thus making a more porous cake whichretains less moisture. The water content of about 40% produces a size ofcrystals which ranges between about lOO and 200 microns in length. Yetadditional HCl cannot be added to the CaCl as such a step wouldsacrifice the recycle HCl needed in the strong leaching step. As can beseen from HQ. 2. the mechanism for diluting the CaCl: comprises drawingoff some (about one-half) of the HC] as part of underflow U6. This isadded to the CaCl in mixer 180. and the gypsum from underflow U6 isseparated in settler I90. The overflow O12 comprising the now dilutedCaCl is carried to the mixer 150 where it is combined with the H. .SO,.The temperature of the mixer 150 can be maintained at 65C cooling.ifnccessary. underflow L 6 from settler l The products of the reactionin mixer [50 go to settler 160 where the HCl is removed and introducedat A2 to drum 20. The gypsum crystals are extracted as underflow L 6,washed and settled by means of overflow 010 to remove remaining HCl.

essentially no phosphate values to be lost. Actual experimental recoveryof the P in the form of diealcium phosphate has been on the order of9092 or higher. A further characteristic of this highly recovereddicalcium phosphate is its purity. That is. conventional processes canbe used to convert this dieal to feed grade phosphoric acid. or furnacegrade acid. "Feed gradephosphoric acid is characterized by the AAFCO ashaving. per each percentage of phosphorus present. no more than lUUppmfluorine. no more than 3.2 ppm arsenic. and no more than 1.3 ppm ofheavy metals reported as lead. Thus. a H;.PO solution which can be madefrom the dical produced as above will have no more than 0.24% by weightfluorine.

1n the above steps. make up water can be used as 15 Turning now to theapparatus utilized in the abovewash water so as to avoid waste streams.described process. FIG. 3 illustrates the details of a rep- Thetemperatures of the above reactions are only resentative crystallizer80. A tank 82 is provided with a slightly above room temperature. thusavoiding the draft tube 84 mounted concentrically with the axis of needfor highly acid-resistant containers and avoiding the tank. from theinside of the tank as by arms 86 vaporization problems. Thus. plasticcontainers can be welded thereto. The pregnant liquor 06 containing theused. The controlling temperatures are those of the acids is added totank 82 via the draft tube. being supcrystallizer and the mixer 150which because of the plied thereto by a pipe 88. The milk of lime issupplied recycling cause the other temperatures to increase centrally oftank 82 via a pipe 90 which feeds into a cup slightly above roomtemperature. Representative tem- 92 mounted on a rotating shaft 94driven by motor 96. peratures and pHs of the various lines andcontainers 35 Near the base of the shaft. holes 98 are provided anddescribed above are as follows: the shaft is joined below cup 92 to ahollow pipe 100 concentrically mounted within the tube 84. Alterna-'lumpcmmw PH tively. pipe 100 and shaft 94 can be an integral piece. Al:UOC 23T U 5 2 At the bottom end of pipe 100, two branches 104 and:[)(:2(' [H 106 are provided. Each branch is illustrated as beingdifferent. but only for purposes of depicting alternate E Q QEEO 5arrangements. Thus. branch 104 is provided with an 114 31 0131 (I 1opening only at the end 105 thereof. while branch 106 is provided withopenings 108 spaced along the upper 117 Ive-55C iii surface thereof. Theangle at which the branches extend from pipe 100 is not critical. Theeffect of either 5 arrangement is to force the milk of lime to riseupui: Kij-jifC 11.1 wardly through a descending column of pregnant li-'f quor. Rotation of the branches additionally causes furii .351 3.55049 ther mixing of the two reactants.

Other apparatus provided in the above Example 4 4mg (H can beconventional. and accordingly is not described 1 It! 50C .5-5.0 herein(oiitainer ll) 311C 1m 4 EXAMPLE 5 3n 30C 0.4 I

This example illustrates the applicability of the invenm 5 m 1 tion tohigh quality phosphate ores. Samples of high so 50C .5-5 quality oresboth as mined and after beneficiation were iii 5 tested in thisexperiment. The samples wee leached for 5 50 30 minutes at ambienttemperatures using 55 millielmiundfiiT quivalents of 3N HCl per gram ofP 0 in the ore (this M C amounts to two parts by weight of hydrogenchloride per part by weight of P 0 The results of these tests It shouldbe emphasized that this preferred example r i hung rcpmted mdlcltwe ofis characterized by a very high level recovery of P 0 as i i lmpunu RockAnal. Leach Soln Hf Recmery Screen i .o,, 11 0;, IP 0. tr-e 0. of P. .0Sample Size Unbeneticiated ()rc 18 mesh 1 1'4 1.19: 4.5: 8159i Lnbene'ficiated Ore llltl mesh 1*. 1" 1.19 392 11% 97.1% Benet'iciated ort- 28mesh 36.5; (14". 5.64; .07? 99.4;

measured from the phosphate in the unbeneficiated ore. That is. theprocess as outlined in FIG. 2 permits It is well known that thebeneficiation step in most conventional wet acid phosphate processesresults in reported herein represent the fourth batch cycle. in orderthat recirculation of the various recirculated ma- The separated leachliquor (387.7 grams at pH 0.8) was heated to 45C and reacted for 12minutes with re cycled precipitated impurities (later described). Thefinal pH ofthe liquor was 0.95. The solids (impurities) were separatedby filtration and washed wtih grams water. The wet filter cake contained2.07 grams water per gram dry cake and dry cake weight was 8.43 grams.This cake contained most of the iron. aluminum and fluoride impuritiesleached from the rock. Liquor. 425.5 grams. pH 0.95. was reacted with34.] grams of milk of lime containing 5. l 1 grams (a0. The reaction wasconducted at 45C for 44 minutes with vigorous agitation. The final pHwas 2.40. 26.75 grams of dry solids containing iron. aluminum andfluoroide impuriterials could bring the process to reasonable cquilib-15 ties were separated by filtration and were recycled for rium.Analytical results on starting materials and varireaction with theliquor as described above. followed ous products are summarized in thesubjoined table. by final removal from the system. The liquor from thisStarting rock was ground to the following screen analyfiltration (39 l.3 grams) was substantially free of iron. I I aluminum and fluorideimpurities.

This liquor was then reacted with grams of milk of lime containing 3.74grams CaO. This brought the pH to 2.87.

LEAcH CALClL'M REGEXERAT ED ()RE INSOLLBLES LIOL'OR PHOSPHATE GYPSL'MHtl P 0. .16; an; 3.43; 4.11140 mun 4.5 giL. CaO 14.24... 7.5% 5.41m34.05'1 saw, 135 Fc. .0 2.54 3.2; new; mai AIUO l 1.44 H1929; 0.ll'1 oyin. F v.57"; (Ll-l'l'i lies, a 3n. sio 51.95% 59.03; 0.41); (l 0.02i0.64'1 8.53: 0.05" l7? ppm Na 1.5m ans; l. i.l- -()l 7.5 K 1.4m (1.17,50 1,30 5.1:; Mg() JUC} .9761 Lot. 7.76; Spgr. l.l2 pH at 25C 0.80

mos;

N mesh 776i V r -f: The reaction was carried out at C for 99 minutes g49 with vigorous agitation. A mixture of anhydrous dicalrn h 15' ciumphosphate and dicalcium phosphate dihydrate 2(J0mesh 7G wasprecipitated. The precipitate was separated by filtration and washedwith 50 grams of water per gram of It will be observed that this screenanalysis shows a dry cake. The dried calcium phosphate weighed 22.17grind in very sharp contradistinction to the grinds typi- 45 grams andcontained 43.0492 P 0 Fluorine content cally used in commercial wetphosphate operations. was only 0.20% This product is suitable for animalwherein the grind is typically 90% through a 200 mesh feed supplements.This represents a final recovery as screen. calcium phosphate of 72% ofthe available P 0 in the A two stage leach was used in which in thefirst stage as-mined rock. The liquor from this step. containing 200grams of fresh rock were leached for 3 minutes 50 mainly calciumchloride was evaporated to 297.] with dilute acid from a subsequentstep. This served grams and reacted with 36.97 grams of 97% sulfuricprincipally to react the carbonates and the very reacacid. The gypsumand hydrochloric acid formed were tive phosphates with the dilutedhydrochloric-phosseparated by filtration. The gypsum was washed withphoric acid mixture. The amount of leach liquor used 100 grams of water.The wet cake contained 1.07 in this operation was 442.3 grams. The leachliquor has grams water per gram of dry cake. 50.5 grams of dry :1 pH of0.43. and the reaction was conducted at ambigypsum were recovered.suitable for fertilizer or conent temperature. The liquor from thisfirst leach step struction products use. The hydrochloric acid was re-(387.7 grams) had a pH of 0.80 and was retained for turned to thestarting process. subsequent recovery of phosphates. The wet cake wasthen reacted with 340 grams of 10% hydrochloric acid EXAMPLE 7 for IDminutes at room temperature. The unreacted In another batch process. theore used in Example 6 material was separated by filtration and washedwith was treated with 3 normal nitric acid. using the same [00 grams ofwater. The filter cake contained 0.36 quantities of acid on a molarbasis. Neutralization was grams of water per gram of dry cake. Dry basiscake effected in two steps using ammonia as the neutralizing weight was170.] grams. The cake. mostly silica. was discarded. The liquor from thefiltration was the material used to react with the fresh rock inrepeating the above-described sequence.

agent. In the first step. impurities were separated from the solublephosphate product. Use of nitric acid appears to have certain advantagesin that ferric phosphate is essentially insoluble in a dilute nitricacid solution. less soluble than it is in a hydrochloric acid solu tion.The second neutralization step separated dical of good quality (49.892 P0 (1.449% fluorine). Recovery of nitrate was effected by treating thefiltrate from the dical recovery with ammonium carbonate. which resultsin removal of residual calcium as calcium carbonate and the formation ofammonium nitrate. This is a valuable by-product as such and may berecovered by evaporation.

In this e\ample the total of acid insolubles. the recovcry of phosphatevalues. and the level of impurities was quite comparable to the resultsshown in Example 6 where hydrochloric acid was used.

What is claimed is:

l. The process of treating apatite-containing ores which comprises:

introducing coarsely ground ore into the first end of a slowly rotatingsubstantially horizontally mounted drum.

introducing introducing into the second end of said drum a 2.34 normalaqueous solution of a mineral acid whose calcium salt is water soluble.

moving said ore and said solution each toward the respective oppositeend of said drum.

removing from said first end spent acid containing dissolved phosphatesand fine particlesize solids. separating the former from the latter.

removing from said second end moist coarse particlcs.

feeding said coarse particles into the first end of a second slowlyrotating substantially horizontally mounted drum. together with a newsupply of said acid. said supply having a normality between about 3 andabout 7.5.

moving said coarse particles and said supply through i said drum to itssecond end. removing said supply and said coarse particles andseparating the one from the other. washing said coarse particles withwater. adding the wash water from said washing step to the separatedfine particles removed from said first end of said first drum.separating the fine particles from said wash water. washing said fineparticles with water. and adding said fine particles wash water to thecoarse particle wash water. the thus further diluted solutionconstituting the said 2.33 normal aqueous mineral acid supplied to saidsecond end of said first drum. 2. The process ofclaim 1 wherein the saidacid is hy drochloric.

3. The process of claim 1 wherein the said acid is ni- INC.

4. The process of claim 1 wherein the ore fed to said first drum issubstantially all minus 30 mesh and at least about two-thirds thereof isplus 100 mesh.

5. The process of claim 1 wherein the ore fed to said first drum isground to a fineness such that substantially all thereof is minusone-eighth inch and not over about ltli thereof is minus 200 mesh.

6. The process ofclaim 1 wherein the said fine particles are separatedfrom the suspending liquid by settling.

7. The process of claim 1 wherein the ore is fed to said first drum by apositive mechanical feeder and is moistened in said feeder with thespent acid solution.

8. The process of claim 1, including:

of further treating the dilute spent acid solution containing dissolvedphosphates by the steps of adding thereto a dilute aqueous suspension ofpH about 6 of which the solids are principally calcium phos phates. inan amount sufficient to bring the pH of said acidic solution to about 3to precipitate calcium phosphate:

separating the precipitate which forms;

washing and drying the same to produce feed grade calcium phosphate;

treating the liquor from said precipitate with lime in an amountsufficient to bring the pH thereof to about 6:

and adding the thus formed suspension to a fresh quantity of said dilutespent acid solution. 9. A process of treating apatite-containing orewhich comprises:

introducing at ambient temperature coarsely ground ore and an about 23normal aqueous solution of a mineral acid whose calcium salt is watersoluble into a first end of a slowly rotating drum slightly inclinedfrom the horizontal. removing from the second end of the drum coarseparticles comprising the ore less the minerals dissolved by the acid insaid drum and fine particles.

removing from the first end of the drum spent acid containing dissolvedphosphates. silicate colloidal solutions. and fine particle-size solids.separating the spent acid and the dissolved phosphates from theparticles and colloidal solution.

feeding the coarse particles and the separated fine particles into thefirst end of a second slowly rotating drum slightly inclined from thehorizontal.

feeding into the second end of said second drum a supply of said acid ofabout 37.5 normality. moving said stronger acid and the coarserparticles counter-current through said second drum. removing the spentstronger acid from the first end of the second drum along with dissolvedphosphates and an amount of fine particles.

removing the last-named fine particles from the spent stronger acid.

and combining the spent stronger acid and dissolved phosphates with thespent dilute acid prior to the removal from the latter of the colloidalsolution.

10. The process as defined in claim 9, and further including the stepsof increasing the pH of the dissolved phosphates after the colloidalsolution has been removed therefrom until dicalcium phosphate hasprecipitated. said increase being accomplished by the addition of a baseselected from the group consisting of lime and ammonia in a manner so asto force the latter to flow counter-current to the flow of dissolvedphosphates. the mixture of the two being gently agitated during saidaddition step.

1 l. The process as defined in claim 9, and further including the stepsof increasing the pH of the dissolved phosphates until dicalciumphosphate has precipitated.

12. The process as defined in claim 11, and further including the stepsof:

forcing water couter-current through the dicalcium phosphate precipitateso as to remove small sized dicalcium crystals therefrom.

separating the small sized dicalcium crystal from the water.

and adding the crystals to the spent stronger acid prior to the removalof the fine particles therefrom 17 so as to raise the pH of the strongeracid until impurities are precipitated out of solution.

[3. The process as defined in claim 12, wherein the pH of the strongeracid is raised by said fine dicalcium phosphate to about 1.

[4. The process as defined in claim 1], and further including the stepsof separating the dicalcium phos phate precipitate from the liquor.mixing into the liquor an equal solution of said mineral acid having thesame normality as said liquor. and adding to said mixture concentrated HSO in a manner so as to rapidly and intimately mix said H 50. and saidmixture together. whereby gypsum and an additional amount of saidmineral acid is produced.

15. The process as defined in claim l4, and further including the stepsof recycling approximately one-half of said produced mineral acid tosaid second drum. and adding the remainder thereto to said liquor.

16. The process as defined in claim 10, and further including the stepsof separating said dicalcium phosphate from the liquor. adding to saidliquor the acid form of said liquor, and mixing into the thus dilutedliquor a solution of H 80 said steps of addition and mixing beingcharacterized by an amount. a rate. and at a temperature sufficient toproduce needle-like gypsum crystals having a crystal size of betweenabout 100 and ZOU microns.

17. The process as defined in claim 9 further including the step ofpassing the colloidal solution and the combined spent acids through agypsum filtering medium to separate colloidal material from the combinedspent acids.

18. The process as defined in claim 12, wherein said step ofprecipitation of impurities includes the step of adding gypsum fines tothe stronger acid in the amount of about 5% by weight of the acid.

19. A process for the recovery of phosphate alues from phosphate oreswhich comprises the steps of:

a. treating a coarsely ground phosphate feed material in two separatestages with an about stoichiometric amount of a dilute mineral acidwhose calcium salt is water soluble, at ambient temperatures. for a timesufficient to extract phosphate. but maintaining the phosphateconcentration at a level not exceeding about 7% P 0 the acid being addedin two separate stages of differing strengths within the range of about27.5 normality. the weaker being added first. and said treatment beingwith substantially non-attritional agitation;

b. treating the leach liquor. containing phosphoric acid. in a firstprecipitation step by raising the pH to about I to 2; and separating theprecipitated impurities;

. treating the liquor in a second precipitation step by raising the pHto a level of about 3 to 5; and separating the high purity calciumphosphate precipitate.

20. The process ofclaim 19 wherein. in step (a). the mineral acid hasnormalities in the range of about 2.3-5.

21. The process ofclaim [9 wherein. in step (a). the phosphateconcentration is maintained in the range of about 34% P 0 22. Theprocess of claim 19 wherein said coarsely ground phosphate feed materialis first moistened with a portion of the leach liquor.

23. The process of claim [9 in which the phosphate feed material istreated with dilute mineral acid whose calcium salt is water soluble intwo slowly rotating substantially horizontally mounted drums.

1. THE PROCESS OF TREATIN APATITE-CONTAINING ORES WHICH COMPRISES: 0INTRODUCING COARSELY GROUND ORE INTO THE FIRST END OF A SLOWLY ROTATINGSUBSTANTIALLY HORIZONTALLY MOUNTED DRUM, INTRODUCING INTRODUCING INTOTHE SECOND END OF SAID DRUM A 2,3-3 NORMAL AQUEOUS SOLUION OF A MINERALACID WHOSE CALCIUM SALT S WATER SOLUBLE, MOVING SAID ORE AND SAIDSOLUTIONEACH TOWARD THE RESPECTIVE OPPOSITE END O SAID DRUM, REMOVINGFROM SAID FIRST END ACID CONTINNG DISSOLVED HOSPHATES AND FINEPARTICLE-SIZE SOLIDS, SEPARATING THE FORMER FROM THE LATTER, REMOVINGFROM SAID SECOND END MOIST COARSE PARTICLES, FEEDING SAID COARSEPARTICLES INTO THE FIRST END OF A SECOND SLOWLY ROTATING SUBSTANTIALLYHORIZONTALLY MOUNTED DOWN, TOGETHER WITH A NEW SUPPLY OF SAID ACID, SAIDSUPPLY HAVING A NORMALITY BETWEEN ABOUT 3 AND ABOUT 7.5, MOVING SAIDCOARSE PARTICLES AND SAID SUPPLY THROUGH SAID DRUM TO ITS SECOND END.REMOVING SAID SUPPLY AND SAID COARSE PARTICLES SEPARATING THE ONE FROMTHE OTHER. WASHING SAID COARSE PARTICLES WITH WATER, ADDING THE WASHWATER FROM SAID WASHING STEP TO THE SEPARATD FINE PARTICLES REMOVED FROMSAID FIRST END OF SAID FIRST DRUM, SEPARATING THE FINE PARTICLES FROMSAID WASH WATER. WASHING SAID FINE PARTICLES WITH WATER, AND ADDING SAIDFINE PARTICLES WASH WATER TO THE COARSE PARTICLE WASH WATER, THE THUSFURTHER DILUTED SOLUTION CONSTITUTING THE SAID, 2,3-3 NORMAL AQUEOUSMINERAL ACID SUPPLIED TO SAID SECOND END OF SAID FIRST DRUM.
 2. Theprocess of claim 1 wherein the said acid is hydrochloric.
 3. The processof claim 1 wherein the said acid is nitric.
 4. The process of claim 1wherein the ore fed to said first drUm is substantially all minus 20mesh and at least about two-thirds thereof is plus 100 mesh.
 5. Theprocess of claim 1 wherein the ore fed to said first drum is ground to afineness such that substantially all thereof is minus one-eighth inchand not over about 10% thereof is minus 200 mesh.
 6. The process ofclaim 1 wherein the said fine particles are separated from thesuspending liquid by settling.
 7. The process of claim 1 wherein the oreis fed to said first drum by a positive mechanical feeder and ismoistened in said feeder with the spent acid solution.
 8. The process ofclaim 1, including: of further treating the dilute spent acid solutioncontaining dissolved phosphates by the steps of adding thereto a diluteaqueous suspension of pH about 6 of which the solids are principallycalcium phosphates, in an amount sufficient to bring the pH of saidacidic solution to about 3 to precipitate calcium phosphate; separatingthe precipitate which forms; washing and drying the same to produce feedgrade calcium phosphate; treating the liquor from said precipitate withlime in an amount sufficient to bring the pH thereof to about 6; andadding the thus formed suspension to a fresh quantity of said dilutespent acid solution.
 9. A process of treating apatite-containing orewhich comprises: introducing at ambient temperature coarsely ground oreand an about 2-3 normal aqueous solution of a mineral acid whose calciumsalt is water soluble into a first end of a slowly rotating drumslightly inclined from the horizontal, removing from the second end ofthe drum coarse particles comprising the ore less the minerals dissolvedby the acid in said drum and fine particles, removing from the first endof the drum spent acid containing dissolved phosphates, silicatecolloidal solutions, and fine particle-size solids, separating the spentacid and the dissolved phosphates from the particles and colloidalsolution, feeding the coarse particles and the separated fine particlesinto the first end of a second slowly rotating drum slightly inclinedfrom the horizontal, feeding into the second end of said second drum asupply of said acid of about 3-7.5 normality, moving said stronger acidand the coarser particles counter-current through said second drum,removing the spent stronger acid from the first end of the second drumalong with dissolved phosphates and an amount of fine particles,removing the last-named fine particles from the spent stronger acid, andcombining the spent stronger acid and dissolved phosphates with thespent dilute acid prior to the removal from the latter of the colloidalsolution.
 10. The process as defined in claim 9, and further includingthe steps of increasing the pH of the dissolved phosphates after thecolloidal solution has been removed therefrom until dicalcium phosphatehas precipitated, said increase being accomplished by the addition of abase selected from the group consisting of lime and ammonia in a mannerso as to force the latter to flow counter-current to the flow ofdissolved phosphates, the mixture of the two being gently agitatedduring said addition step.
 11. The process as defined in claim 9, andfurther including the steps of increasing the pH of the dissolvedphosphates until dicalcium phosphate has precipitated.
 12. The processas defined in claim 11, and further including the steps of: forcingwater couter-current through the dicalcium phosphate precipitate so asto remove small sized dicalcium crystals therefrom, separating the smallsized dicalcium crystal from the water, and adding the crystals to thespent stronger acid prior to the removal of the fine particles therefromso as to raise the pH of the stronger acid until impurities areprecipitated out of solution.
 13. The process as defined in claim 12,wherein the pH of the stronger acid is raised by said fine dicalciumphosphate to about
 14. The process as defined in claim 11, and furtherincluding the steps of separating the dicalcium phosphate precipitatefrom the liquor, mixing into the liquor an equal solution of saidmineral acid having the same normality as said liquor, and adding tosaid mixture concentrated H2SO4 in a manner so as to rapidly andintimately mix said H2SO4 and said mixture together, whereby gypsum andan additional amount of said mineral acid is produced.
 15. The processas defined in claim 14, and further including the steps of recyclingapproximately one-half of said produced mineral acid to said seconddrum, and adding the remainder thereto to said liquor.
 16. The processas defined in claim 10, and further including the steps of separatingsaid dicalcium phosphate from the liquor, adding to said liquor the acidform of said liquor, and mixing into the thus diluted liquor a solutionof H2SO4, said steps of addition and mixing being characterized by anamount, a rate, and at a temperature sufficient to produce needle-likegypsum crystals having a crystal size of between about 100 and 200microns.
 17. The process as defined in claim 9 further including thestep of passing the colloidal solution and the combined spent acidsthrough a gypsum filtering medium to separate colloidal material fromthe combined spent acids.
 18. The process as defined in claim 12,wherein said step of precipitation of impurities includes the step ofadding gypsum fines to the stronger acid in the amount of about .5% byweight of the acid.
 19. A PROCESS FOR THE RECOVERY OF PHOSPHATE VALUESFROM PHOSPHATE ORES WHICH COMPRISES THE STEPS OF: A. TREATING A COARSELYGROUND PHOSPHATE FEED MATEIAL IN TWO SEPARATE STAGES WITH AN ABOUTTIOCHIOMETRIC AMOUNT OF A DILUTE MINERAL ACID WHOSE CALCIUM SALT ISWATER SOLUBLE, AT AMBIENT TEMPERATURES, FOR A TIME SUFFICIENT TO EXTRACTPHOSPHATE, BUT MAINTAINING THE PHOSPHAE CONCENTRTION AT A LEVEL NOTEXCEEDING ABOUT 7% P25, THE ACID BEING ADDED IN TWO SEPARATE STAGES OFDIFFERING STRENGTHS WITHIN THE RANGE OF ABOUT 2-7.5 NORMALITY, THEWEAKER BEING ADDED FIRST, AND SAID TREATMENT BEING WITH SUBSTANTIALLYNON-ATTRITIONAL AGITATION, B. TREATING THE LEACH LIQUOR, CONTAININGPHOSPHERIC ACID, IN A FIRST PRECIPITATION STEP BY RAISING THE PH TOABOUT 1 TO 2, ANDD SEPARATING THE PRECIPITATED IMPURITIES, C. TREATINGTHE LIQUOR IN A SECOND PRECIPITATION STEP BY RAISING THE PH TO A LEVELOF ABOUT 3 TO 5, AND SEPARATING THE HIGH PURITY CALCIUM PHOSPHATEPRECIPITATE.
 20. The process of claim 19 wherein, in step (a), themineral acid has normalities in the range of about 2.3-5.
 21. Theprocess of claim 19 wherein, in step (a), the phosphate concentration ismaintained in the range of about 3-5% P2O5.
 22. The process of claim 19wherein said coarsely ground phosphate feed material is first moistenedwith a portion of the leach liquor.
 23. The process of claim 19 in whichthe phosphate feed material is treated with dilute mineral acid whosecalcium salt is water soluble in two slowly rotating substantiallyhorizontally mounted drums.